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At least 883 records · Page 49
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NASA NTRS1985

Halite particles injected into the stratosphere by the 1982 El Chichon eruption

A cascade impactor was flown on board a U-2 aircraft to gather particulate samples in the stratosphere at 18-21 km altitude after the El Chichon eruptions of 1982. Halite particles were observed, which posed a hazard for the catalytic destruction of ozone. No halite particles were observed a month after the eruptions, while a 40 percent increase in HCl was detected at 12 km, an increase which could have been augmented by halite transformations. The halite proportion of the volcanic clouds was of the same proportion of NaCl as in the volcanic ash around El Chichon. The results indicate that halite forms in eruption clouds of volcanos with alkalic magmas.

Woods, D. C.↗
NASA NTRS1985

SNC meteorites - Clues to Martian petrologic evolution?

Shergottites, nakhlites and the Chassigny meteorites (SNC group) may have originated on Mars. The shergottites are medium-grained basalts, the nakhlites are pyroxenites and the Chassigny is a dunite. The SNC group is petrologically diverse but differs from all other known achondrites in terms of mineral chemistry, the redox state, the oxygen isotopic composition and the radiometric ages. The SNC stones are mafic and ultramafic cumulate rocks with mineralogies that indicate rapid cooling and crystallization from tholeiitic magmas which contained water and experienced a high degree of oxidation. The characteristics suggest formation from a large parent body, i.e., a planet, but not earth. The estimated ages for the rocks match the estimated ages for several mapped Martian volcanoes in the Tharsis region. Additionally, the elemental and isotopic abundances of atmospheric gases embedded in melts in the SNC stones match Viking Lander data for the Martian atmosphere. However, reasons are cited for discounting the possibility that a large meteorite(s) collided with Mars about 180 myr ago and served as the mechanism for ejecting the SNC stones to earth.

Mcsween, H. Y., Jr.↗
NASA NTRS1985

Lunar and Planetary Science Conference, 16th, Houston, TX, March 11-15, 1985, Proceedings. Part 1

Various papers on lunar studies, meteorites and cosmic dust, Mars, and tektites are presented. The topics discussed include: very high potassium basalt; complications in mare basalt petrogenesis; mare basalt genesis; modeling trace elements and isotopic ratios; Zr-Hf-Ta fractionation during lunar evolution; petrology of the Apollo 12 highland component; petrologic province maps of the lunar highlands derived from orbital geochemical data; petrology and chemistry of Apollo 12 regolith breccias; chemical variability and origin of agglutinitic glass; multistage exposure history of the 74261 soil constituents; and an experimental investigation of agglutinate melting mechanisms; shocked mixtures of sodium and potassium feldspars. Also addressed are: cooling history of some Antarctic ureilites; the Leoville accretionary breccia; ubiquitous brecciation after metamorphism in equilibrated ordinary chondrites; layer silicates in a chondritic porous interplanetary dust particle; estimates of rheological properties for flows on the Martian volcano Ascraeus Mons; the Martian dust storm of Sol 1742; and late Eocene North American microtektites and clinopyroxene-bearing spherules.

Ryder, G.↗
NASA NTRS1986

Effect of the greenhouse gases (CO2, H2O, SO2) on Martian paleoclimate

There is general agreement that certain surface features on Mars are indicative of the presence of liquid water at various times in the geologic past. In particular, the valley networks are difficult to explain by a mechanism other than the flow of liquid water. It has been suggested in several studies that a thick CO2 atmosphere on Mars early in its history could have provided a greenhouse warming that would have allowed the flow of water either on the surface or just below the surface. However, this effect was examined with a detailed radiation model, and it was found that if reduced solar luminosity early in the history of the solar system is taken into account, even three bars of CO2 will not provide sufficient greeenhouse warming. The addition of water vapor and sulflur dioxide (both plausible gases that may have been emitted by Martian volcanoes) to the atmosphere also fail to warm the surface above 273 K for reduced solar luminosity conditions. The increase in temperature may be large enough, however, for the formation of these features by brines.

Postawko, S. E.↗
NASA NTRS1986

Cosmogenic helium in a terrestrial igneous rock

New helium isotopic measurements on samples from the Kula formation of Haleakala volcano of Hawaii are presented that are best explained by an in situ cosmogenic origin for a significant fraction of the He-3. Results from crushing and stepwise heating experiments, and consideration of the exposure age of the sample at the surface and the cosmic ray fluxes strongly support this hypothesis. Although crustal cosmogenic helium has been proposed previously, this represents its first unambiguous identification in a terrestrial sample.

Kurz, M. D.↗
NASA NTRS1986

Observed perturbations of the Earth's Radiation Budget - A response to the El Chichon stratospheric aerosol layer?

The Earth Radiation Budget experiment, launched aboard the Nimbus-7 polar-orbiting spacecraft in late 1978, has now taken over seven years of measurements. The dataset, which is global in coverage, consists of the individual components of the earth's radiation budget, including longwave emission, net radiation, and both total and near-infrared albedos. Starting some six months after the 1982 eruption of the El Chichon volcano, substantial long-lived positive shortwave irradiance anomalies were observed by the experiment in both the northern and southern polar regions. Analysis of the morphology of this phenomena indicates that the cause is the global stratospheric aerosol layer which formed from the cloud of volcanic effluents. There was little change in the emitted longwave in the polar regions. At the north pole the largest anomaly was in the near-infrared, but at the south pole the near UV-visible anomaly was larger. Assuming an exponential decay, the time constant for the north polar, near-infrared anomaly was 1.2 years. At mid- and low latitudes the effect of the El Chichon aerosol layer could not be separated from the strong reflected-shortwave and emitted-longwave perturbations issuing from the El Nino/Southern Oscillation event of 1982-83.

Ardanuy, P. E.↗
NASA NTRS1986

SIR-B radar imagery of volcanic deposits in the Andes

Synthetic-aperture radar imagery from the Shuttle Imaging Radar - mission B (SIR-B) was collected in October 1984 over the central Andes between 20 deg S and 24 deg S and also south of 42 deg S. Despite signal-strength problems that drastically reduced the signal-to-noise ratio of the images, volcanic features of both areas show up well. In particular, ignimbrite sheets formed by large explosive eruptions stand out as very strong radar reflectors. High backscatter is apparently caused by erosional relief on the ignimbrites at scales ranging from the radar wavelength (23 cm for SIR-B) to the 30-200-m scale of quebradas (gullies and canyons). The consistent regional erosional pattern appears unrelated to the emplacement of the ignimbrites, and is probably caused by preferential eolian erosion in the directions of the prevailing wind. Hand-held space photographs, ground observations, and Landsat Thematic Mapper imagery support the interpretation of the ignimbrite radar signature. The Chilean volcano Michinmahuida was imaged by four radar data takes at different incidence angles, which show tectonic, glacial, and volcanic features of that nearly inaccessible and often cloud-covered region. Stereo viewing of radar images from two data takes greatly enhances the geologic interpretation of this rugged area.

Fielding, E. J.↗
NASA NTRS1985

An evaluation of the performance of Umkehr stations by Solar Backscattered Ultraviolet (SBUV) experiment

Until recently, Umkehr data taken by 20 Dobson stations around the world have been the principal source of information about the behavior of upper stratospheric ozone. Umkehr results are used also for detecting drifts in satellite instruments and for determining intersatellite biases. However, a systematic evaluation of the quality of Umkehr data taken by the various stations has been lacking. Five years of ozone profile data from the Solar Backscattered Ultraviolet (SBUV) have been used to examine and intercompare the quality of Umkehr stations, and to assess the degradation of their performance after the El Chichon volcano eruption in southern Mexico. In contrast to Umkehr, the SBUV ozone measurments in layers 7 through 9 (1-8 mb) were unaffected by the massive amounts of dust and gases ejected by El Chichon.

Bhartia, P. K.↗
NASA NTRS1986

Lidar observations of the decline of the El Chichon stratospheric load

The eruption of the Mexican volcano El Chichon in Apr. 1982 enhanced the stratospheric aerosol load to a level which so far has not been observed by remote sensing techniques. The ruby lidar system at Garmisch-Partenkirchen recorded an increase of about two orders of magnitude above the background level of the years 1977/78. At northern midlatitudes backscattering was peaking in Jan./Feb. 1983, as illustrated. The decline of the El Chichon stratospheric perturbation is discussed. The decay of the El Chichon stratospheric cloud is characterized by an overall 1/e lifetime of about 12 months. The El Chichon decay is further characterized by seasonal variations of the integral backscattering coefficient, which exhibit a winter maximum and a summer minimum. These variations are inversely correlated with the seasonal mean movement of the tropopause height indicating transport processes.

Jaeger, H.↗
NASA NTRS1986

On the relationship between age of lava flows and radar backscattering

The observation that older lava flows have lower backscatter in radar images is assessed with multiwavelength/polarization scatterometer data with incidence angles from 15 to 50 deg. Backscatter decreases over time because surface roughness decreases due to infilling with dust and mechanical weathering of the rocks. Pahoehoe lavas in the Snake River Plain with ages of 2.1, 7,4, and 12.0 K yr are best separated with 2.25 cm wavelength data. Blocky obsidian flows at Medicine Lake Highland and Newberry Volcano with ages of 0.9, 1.1 and 1.4 K yr are best separated with 6.3 cm wavelength data. Two Pleistocene flows at the Snake River Plain are best separated with 19.0 cm wavelength data. Incidence angles from 20 to 35 deg are best. These data indicate it may be possible to separate lava flows into eruptive periods using calibrated multiwavelength radar backscatter data.

Blom, R. G.↗
NASA NTRS1987

Water and ice on Mars: Evidence from Valles Marineris

An important contribution to the volatile history of Mars comes from a detailed study of Valles Marineris, where excellent stereoimages and a three-dimensional view of the upper Martian crust permit unusual insights. The evidence that ground water and ice existed until relatively recently or still exist in the equatorial area comes from observations of landslides, wall rock, and dark volcanic vents. Valles Marineris landslides are different in efficiency from large catastrophic landslides on Earth. One explanation for the difference might be that the Martian slides are lubricated by water. A comparison of landslide speeds also suggests that the Martian slides contain water. That Valles Marineris wall rock contained water or ice is further suggested by its difference from the interior layered deposits. Faults and fault zones in Valles Marineris also shed light on the problem of water content in the walls. Because the main evidence for water and ice in the wall rock comes from landslides, their time of emplacement is important. The landslides in Valles Marineris date from the time of late eruptions of the Tharsis volcanoes and thus were emplaced after the major activity of Martian outflow channels. None of the observations conclusively demonstrate that water or ice existed in the wall rock of Valles Marineris, but altogether the evidence is highly suggestive.

Lucchitta, B. K.↗
NASA NTRS1987

Studies of vesicle distribution patterns in Hawaiian lavas

Basaltic lava flows are generally vesicular, and the broader facts relating to vesicle distribution have long been established; few studies have yet been made with a view to determining how and when vesicles form in the cooling history of the lava, explaining vesicle shape and size distribution, and gaining enough understanding to employ vesicles as a geological tool. Various avenues of approach exist by which one may seek to gain a better understanding of these ubiquitous structures and make a start towards developing a general theory, and three such avenues have recently been explored. One avenue involves the study of pipe vesicles; these are a well known feature of lava flows and are narrow pipes which occur near the base of many pahoehoe flow units. Another avenue of approach is that presented by the distinctive spongy pahoehoe facies of lava that is common in distal locations on Hawaiian volcanoes. A third avenue of approach is that of the study of gas blisters in lava. Gas blisters are voids, which can be as much as tens of meters wide, where the lava split along a vesicle-rich layer and the roof up-arched by gas pressure. These three avenues are briefly discussed.

Walker, George P. L.↗
NASA NTRS1987

Geology of the Mohon Mountain volcanic field, Yavapai and Mohave Counties, Arizona: A preliminary report

Field mapping has produced a preliminary picture of Mohon Mountain as a composite volcano, in which pyroclastic ash and larger tephra erupted alternately with flows of rhyodacite and dacite. An analog study which uses imagery of lunar and Martian features will compare the overall shape of the vent complex, including its breached southern flank and satellite vents, to similar landforms found on Mars and the Moon which are believed to have formed similar processes. Ash flow sheets were hypothesized to comprise the outer slopes of Olympus Mons suggesting that explosive eruptions which are more volatile-rich than those which produce basalt flows are not confined to terrestrial settings but may also be found on bodies such as Mars, which have a thicker crust and deeper magma source in the mantle. The analog study will explore further evidence for explosive eruptions on Mars and the Moon.

Simmons, Ardyth M.↗
NASA NTRS1987

Implications of Viking color data for evolution of the Amenthes Region, Mars

In the Eastern Hemisphere of Mars, where the hemispheric dichotomy is not overlain by relatively recent flows from the Tharsis volcanoes, the Mars cratered terrain boundary (CTB) now exists as highly fractured terrain juxtaposed with the smooth plains of the Northern Hemisphere. Based on Mariner 9 photography, the southern cratered terrain in the Amenthes region (0 to 30 deg N, 225 to 270 deg W) is approximately 3 to 4 km above the northern plains, and the transition zone is marked by both broad plateaus and knobby terrain. In the Amenthes Southest quadrangle, in particular, the continuum between large detached plateaus, smaller smooth topped plateaus and knobby hills can be seen. To define the previous position and evolution of the boundary, the distribution of cratered terrain, characteristic landforms (knobby terrain and detached plateaus) have been mapped, as well as structural features across the boundary. Structural mapping indicates that geological formations parallel the boundary in the Eastern Hemisphere with the conclusion that CTB evolution involved normal faulting through extension perpendicular to the boundary.

Maxwell, Ted A.↗
NASA NTRS1987

Stress history of the Tharsis Region, Mars

The Tharsis topographic rise of Mars is roughly 5000 km wide and 10 km high and is believed to have originated more than 3.5 BY ago. Within its boundaries lie the four largest volcanoes on the planet. It is also the locus of a series of fracture traces which extend over approximately a hemisphere. The events leading to the formation of the Tharsis region continue to generate debate. Three geophysical models of the formation of Tharsis are now in general contention and each of these models has been used to predict a characteristic stress-field. These models are: the volcanic construct model, the isostatic compensation model, and the lithospheric uplift model. Each has been used by its proponents to predict some of the features observed in the Tharsis region but none accurately accounts for all of the fracture features observed. This is due, in part, to the use of fractures too young to be directly related to the origin of Tharsis. To constrain the origin of Tharsis, as opposed to its later history, one should look for the oldest fractures related to Tharsis and compare these to the predictions made by the models. Mapping of old terrains in and around the Tharsis rise has revealed 175 hitherto unknown old fracture features.

Francis, Robert A.↗
NASA NTRS1987

The origin of channels and associated deposits in the Elysium region of Mars

Photogeological studies of the Elysium volcanic province of Mars show that its sinuous channels are part of a large deposit which probably was emplaced as a series of huge volcanic debris flows or lahars. The suggestion is based on evidence that the lahars were : (1) gravity-driven mass flow deposits (lobate outlines, steep snouts, smooth medial channels and rough lateral deposits--the deposits narrow and widen in accord with topography, and they extend downslope); (2) wet (channeled surfaces, drainage features); and (3) associated with volcanism (the deposits and channels extend from a system of fractures which fed lava flows). It is conceivable that heat associated with magmatism melted ground ice below the Elysium volcanoes, formed a muddy slurry which issued out of regional fractures and spread over the adjoining plain.

Christiansen, Eric H.↗
NASA NTRS1986

Dispersion characteristics of volcanically injected aerosol as seen by SAGE I, SAM II, and SAGE II

General features of the dispersion of aerosols injected into the atmosphere by volcanic eruptions are described on the bases of data from the SAGE I, SAGE II and SAM II satellites. All three satellites carried sensors which measured the vertical profile of aerosol extinction at 1 micron wavelength. The discussion covers the eruptions of seven volcanoes over the period 1979-82. The events occurred at low latitudes and in the Northern Hemisphere. Aerosols from Northern Hemisphere eruptions stayed in the Northern Hemisphere, while aerosols from low latitude events spread to both hemispheres. Dispersion was fastest in the winter hemisphere. Sample details are discussed from tracking the dispersion of the aerosol from the eruption of El Chichon by SAGE II sensors.

Kent, G. S.↗
NASA NTRS1986

Retrieval of aerosol size distribution moments from multiwavelength particulate extinction data

An iterative method for deriving the particle size distribution from multiwavelength satellite remote sensing data is presented and its use illustrated with an application to SAGE II data. The compression size distribution method (CSD) features interpolation and look-up features for relating the coefficients of a least-squares fit as a function of wavelength to parameters of the compression function that have been obtained by Mie calculations. Results are reported of comparisons between particulate radii predicted for the El Chichon volcano aerosol based on SAGE II data and 14 radii measured with NASA flights through the aerosol with aircraft carrying wire impactors.

Livingston, J. M.↗